Fix integer overflow in utf{16,32}_to_utf8_length am: c17624db am:...

Fix integer overflow in utf{16,32}_to_utf8_length am: c17624db am: 3065de2c  -s ours am: c282fe5c  -s ours am: 47dfd5af  -s ours am: fc4b272a  -s ours am: 069ec60f  -s ours am: 3c374a2b  -s ours am: cee1faef  -s ours am: 8ecef89e  -s ours
am: 78a6b7e2  -s ours

Change-Id: Ibf9e0a5b62304069c3d88742e1215b9783435391